This lecture covers the resolution of question 1 of series 19, focusing on interference in a two-slit interference device with polarizers oriented perpendicular and parallel to the slits. It explains how the interference pattern on the screen depends on the electric field intensity, which is proportional to the square of the electric field amplitude. By analyzing the intensities of the two sources and the interference term, it concludes that in this specific case, where the polarizers have perpendicular axes, there is no interference observed. The instructor clarifies the concept of interference in polarized light and encourages questions from the audience.